This invention relates to a hydraulic power trim and shock absorbing supply system for marine propulsion devices.
Outboard motors, stern drive units and the like employ a vertically tiltable lower propeller units which are adjustable trimmed relative to the boat and water. Generally, adjustable trimming means is required to compensate for various factors such as speed, loading, water conditions and the like. Proper trimming is desirable in order to obtain maximum speed operation while maintaining safe propulsion conditions. As various factors may vary when underway, this system desirably provides for adjustment of the trim while moving.
Generally, the support and lower units are provided with piston-cylinder units connected to a suitably pressurized fluid supply for trim adjustment. Additionally, hydraulic shock absorbing and energy dissipating piston-cylinder units are employed to permit tilt of the lower unit in response to striking of an underwater obstacle and the like without damage to the boat or motor. Further for trailering and maintenance, the propulsion device is tilted upwardly to a clearance position. Various systems have been suggested employing separate trim position units and shock absorbing units.
Generally, known functioning units include suitable shock valve means connected in the system to compensate for timed energy forces under impact. For example, an energy absorbing relief valve means may be provided in the pump unit. Because of the large forces and pressures encountered, however, the size, shape, and structure of the hydraulic lines and connections become critical. The hydraulic system normally includes flexible lines or hoses for convenient interconnection of an inboard reservoir and pump means to the hydraulic actuator. Such lines are inherently subject to expansion and contraction under the required high pressures which may adversely affect the system operation. In addition, very large high strength lines are required. A highly desirable system employs a dual acting piston-cylinder unit for trim positioning, trailering positioning, and shock absorbing. The use of a combined shock absorbing and a trim positioning cylinder unit minimizes the number of components thereby minimizing the hardwar and undesirable asethetics associated with the multiple component systems. An extremely satisfactory system is disclosed in Applicant's copending application entitled "HYDRAULIC POWERED TRIM AND TILT APPARATUS FOR MARINE PROPULSION DEVICES"chich was filed on the same date as this application and is assigned to a common assignee herewith. As more fully disclosed in such application, the combined trim, tilt, and shock absorbing means is provided mounted within the bracket assembly for aesthetic purposes and also to protect the components and particularly the hydraulic connections.
In the prior art systems, it is also possible that the velocity at impact will not be great enough to release the delicate absorbing system because it is below the break-loose level. However, the impact may be sufficient to, at least temporarily, stop the boat; with the possibility of danger to the passengers as a result of being thrown forward and the like.
The trim system is also preferably provided with a "trail-out" circuit which permits the unit to ride over obstructions at low speeds and also permits manual tilting of the lower unit.
Further, with impacting and energy absorbing devices, in combination with the variable trim control, the motor should preferably automatically return to the previously established trim position. This of course requires that a "memory" be introduced into the system.
In order to permit the various functions under optimum conditions relatively complicated hydraulic systems and multiple cylinder arrangements have been generally employed.